Group-directed communications are commonplace in enterprise and public safety communication systems. With regard to voice communications, one end device directs an audio stream (i.e., a “talkburst”) to a given group (i.e. a “talkgroup”) of receiving end devices. These receiving end devices reproduce the audio stream through an amplified speaker. The manner in which the receiving end devices operate usually results in the reproduced sound being audible to people other than merely the intended recipient. Typically, in these group-based systems, the receiving end devices are located near each other, causing their associated listeners to hear the same audio stream reproduced by multiple end devices. This is particularly true in public safety uses, in which personnel often respond to incidences in a group and this group (or a subset thereof) is located in the same local area for an extended period of time.
In order to ensure the audio stream is intelligible to the intended listeners in such an environment, it is desirable for collocated devices to reproduce the audio stream in a time synchronized fashion. In other words, it is desirable for all speakers in the collocated devices to reproduce the same audio waveform at roughly the same time. In practice, a temporal offset of about 30 ms or so between multiple audible speakers reproducing the same waveform is virtually undetectable to most listeners.
Synchronization methods for the homogeneous circuit-based wireless radio area networks (RANs) of the current generation of enterprise and public safety communication systems are unlikely to provide acceptable results in future generations of RANs, which are likely to span multiple narrowband circuit-switched and broadband packet-based broadband technologies. A variety of delays exist in such networks causing spreading and jitter problems. Sources of these problems include different amounts of time for different destination end devices to be paged and activated, packet duplication and retries in broadband wireless networks, and multitasking processing delays. Without a mechanism to compensate for the combined new and existing sources of destination-specific delay and jitter, each end device will reproduce audio in an autonomous fashion. This results in unintelligibility when two or more end devices are collocated.